The squeaking is caused by the joints not being firmly glued and wood rubbing against wood. Ideally, you should locate the offending joints, separate and reglue them. Short of that, it might be possible , if the gap is large enough, to let glue run down into the joint to stabilize it. Normal capenters glue requires a rather close fit of the parts. If a large gap is present, using a two part epoxy glue in a syringe type appplicator might fill the gap and stop the rubbing. Such epoxy syringes are available in the paint department at Home Depot. They have a spiral tip which has the two parts mixed by the time it reaches the tip. The tip also allows you to concentrate the application to the offending gap. Epoxy has its own structural integrity and can reinforce a void.